The present invention relates to a plasma deposition welding powder for the production of wear-resistant layers on machine parts which are subject to friction, and more particularly, to a plasma deposition welding powder for producing wear-resistant layers on sealing strips in rotary engines and piston rings of piston engines, particularly those made preferably of cast iron which is rich in carbon and silicon.
The friction partners which seal the combustion chamber of a rotary engine are the chamber walls of the rotary engine which have a trochoidal shape and the sealing strips which are disposed at the corners of the rotary engine rotor. Sealing strips in rotary engines are subject to high operation pressures and temperatures during running of the engine as well as to high friction stresses with possibly insufficient lubrication and high corrosion stresses. It is therefore necessary to provide the sealing strips with wear-resistant surfaces in their area of greatest stress, i.e., in the area where they contact the trochoidal chamber wall. Care must be taken, however, that low-wear movement is assured for both of the friction partners which seal the combustion chambers, i.e., the sealing strip and the trochoidal chamber walls, so that mutual compatibility of the sealing strips and trochoidal chamber walls is necessary.
Protective layers or coatings have been used for the contact surfaces of the trochoidal chamber walls and such layers which have been found satisfactory in practice are, particular, electrolytically-deposited hard chromium layers, electrolytically-deposited nickel layers with embedded silicon carbides, and thermal spray layers. All of these layers, however, are inherently very wear-resistant and thus heavily attack their friction partners (the sealing strips) due to their high hardness. Thus, the sealing strip material which contacts the trochoidal chamber wall must be a material which is compatible with the trochoidal chamber wall coating and which has a wear-resistance that assures perfect operation. In one prior art technique, sealing strips which are made entirely of a material which can withstand such stresses without wear are known and can be produced, but either their breaking and bending strength is too low or they are too expensive so that economical use of such materials is not worthwhile.
In another prior art technique, the contact surfaces of the sealing strip have been provided with protective coatings according to known coating methods. For example, thermal spray layers have been applied to the contact surfaces of sealing strips, but were found to be ineffective due to the layer stability being too low. In addition, chemical reaction layers, chemical vapor-deposited (CVD) layers and vapor-deposited layers have been tried as protective layers for the contact surfaces of sealing strips, but were found unsatisfactory due to poor adhesion and layer thickness. Moreover, electrodeposited layers have been tried as protective coatings for the contact surfaces of sealing strips, but have been found to be unsatisfactory because of their poor wear-resistance.
Wear-resistant layers applied by plasma deposition welding have been used as protective coatings for the contact surfaces of sealing strips and overcome the above-mentioned drawbacks, but the deposition welding powder of molybdenum and/or tungsten, possibly with the addition of metallic alloys previously used for such purposes, forms coating layers on the contact surfaces of sealing strips which have poor compatibility with the contact surface coatings of the trochoidal chamber walls, particularly if these are made of electrodeposited nickel layers with silicon carbides embedded therein. Grooves are formed on the friction surfaces and, after longer periods of use, the engine malfunctions.